Advertise Mag reading when button pushed

[espruino-discuss]

Posted at 2017-02-15 by Terrence

Is there a tutorial, that I can't find, that shows code to advertise the magnetometer values in a characteristic when the button is pushed?

Thank you.

[gfwilliams]

Posted at 2017-02-15 by @gfwilliams

There isn't, but try:

setWatch(function() {
  var m = Puck.mag();
  NRF.setAdvertising({
    0x1809 : [m.x>>8,m.x,m.y>>8,m.y,m.z>>8,m.z]
  });
}, BTN, {repeat:true,debounce:50,edge:"rising"});

That should pack the magnetometer data into 6 bytes that you could then read. Hope that helps!

[espruino-discuss]

Posted at 2017-02-15 by Terrence

Thank you for the code sample, I will put it into place tonight.

[espruino-discuss]

Posted at 2017-02-24 by user73560

Hi Gordon,

On Puck we have: [-21, -5126,5,1289, -3,-747]
On RPi3 we have: [235, 250,5, 9,253, 21]

How can we obtain the advertised mag values ?

[gfwilliams]

Posted at 2017-02-24 by @gfwilliams

In JavaScript?

It seems I got the endianness wrong, so you can't just do: new Int16Array((new Uint8Array([235, 250,5, 9,253, 21])).buffer)

Instead you need:

var a = [235, 250,5, 9,253, 21];
var d = [(a[0]<<8)|a[1], (a[2]<<8)|a[3], (a[4]<<8)|a[5]];
for (var i=0;i<3;i++) if (d[i]&32768) d[i]-=65536;
// results in d

I guess you're using Java in Android - that code should be pretty easy to convert.

There are other ways of converting numbers from byte arrays (utilities in various different languages), but the code above is pretty universal.

[espruino-discuss]

Posted at 2017-02-25 by user73560

Hi Gordon,

Thank you for your answer. Yes, one way of getting the data on Android is:

int value = new BigInteger(new byte[]{a[i], a[i + 1]}).intValue();

[espruino-discuss]

Posted at 2017-04-27 by Tineler

Hi @gfwilliams

How did you test the advertising? I'm trying to test it using a WiPy and the nRF connect app, but I don't see any data.

[gfwilliams]

Posted at 2017-04-27 by @gfwilliams

Personally I use the NRF Connect app to scan for advertising data.

You're trying to scan for advertising data that's coming from a Puck.js?

Are you disconnected from the Puck.js? Puck.js (like most BLE devices) will only advertise when there is no device with an active BLE connection to it.

[espruino-discuss]

Posted at 2017-04-27 by Tineler

Yes, I'm trying to scan for advertising data that's coming from my Puck.js.

I indeed had a Bluetooth connection open (for the IDE). Thank you!